by D EP · Cited by 2 — Fans that generate high airflow at relatively low speeds (for example, forward-curved blade centrifugal fans) require a relatively accurate estimate of the

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TOFENERGYDEPARTMENUENITEDSTATSOFAERICAMImproving Fan System Performance a sourcebook for industry U.S. Department of EnergyEnergy Efficiency and Renewable EnergyOne of a series of industrial energy efficiency sourcebooksa sourcebook for industry Bringing you a prosperous future where energy is clean, abundant, reliable, and affordableImproving Fan System Performance

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AcknowledgmentsImproving Fan System Performance: A Sourcebook for Industry has been developed by the U.S. Departmentof EnergyÕs (DOE) Industrial Technologies Program and the Air Movement and Control Association International, Inc. (AMCA), a DOE Allied Partner. Industrial Technologies and AMCA International undertook this project as part of a series of sourcebook publications on motor-driven equipment under the BestPractices effort. Other topics in this series include compressed air systems, pumping systems, and motors and drives. For more information about the Industrial TechnologiesÕ BestPractices effort and AMCA International, see Section 3.AMCA International is a not-for-profit association of the worldÕs manufacturers of related air system equipmentÑprimarily, but not limited to fans, louvers, dampers, air curtains, airflow measurement stations, acoustic attenuators, and other air system componentsÑfor industrial, commercial, and residential markets. The associationÕs mission is to promote the health and growth of industries covered by its scope and the members of the association consistent with the interests of the public.DOE, AMCA International, Lawrence Berkeley National Laboratory, and Resource Dynamics Corporation thank the staff at the many organizations that so generously assisted in the collection of data for this sourcebook. The contributions of the following participants are appreciated for their review and input to this sourcebook: Gary Benson, The New York Blower Company Frank Breining, Airmaster Fan Company Don Casada, Diagnostic Solutions, LLC Brad Gustafson, U.S. Department of Energy Tom Gustafson, Hartzell Fan, Inc.Tony Quinn, American Fan Company & Woods USA Division Paul Saxon, Air Movement and Control Association International, Inc. Bill Smiley, The Trane Company Sastry Varanasi, ABB Fan Group North America Dick Williamson, Twin City Fan Companies, Ltd. Ron Wroblewski, Productive Energy Solutions Prepared for:The United States Department of Energy Air Movement and Control Association International, Inc.Prepared by:Lawrence Berkeley National Laboratory Washington, DCResource Dynamics Corporation Vienna, VA Cover photo credit:Copyright ©CML Northern Blower Inc., 1989. All rights reserved. This image may not be reproduced, stored, or transmitted in any form or means without the prior written consent of the copyright holder.

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Quick Start GuideSection 1: Introduction to Fan SystemsFans3 Fan Performance Curves6 Fan System Components9 Section 2: Performance Improvement Opportunity Roadmap1ÑAssessing Fan System Needs17 2ÑFan Types19 3ÑBasic Maintenance25 4ÑCommon Fan Systems Problems29 5ÑIndications of Oversized Fans33 6ÑSystem Leaks37 7ÑConfigurations to Improve Fan System Efficiency39 8ÑControlling Fans with Variable Loads43 9ÑFan Drive Options47 10ÐMultiple-Fan Arrangements51 11ÐFan System Economics55 Section 3: Programs, Contacts, and ResourcesIndustrial Technologies Program and BestPractices59 Air Movement and Control Association International, Inc. (AMCA International)63 Directory of Contacts65 Resources and Tools67 AppendicesAppendix A: Fan System Terminology75 Appendix B: The Fan System Marketplace83 iA Sourcebook for Industry Contents13155975

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1A Sourcebook for Industry This sourcebook is designed to provide fan system users with a reference outlining opportunities to improve system performance. It is not intended to be a comprehensive technical text on improving fan systems, but rather a document that makes users aware of potential performance improvements, provides some practical guidelines, and details where the user can find more help. The sourcebookis divided into three main sections and appendices.Section 1: Introduction to Fan SystemsFor users unfamiliar with the basics of fans and fansystems, a brief discussion of the terms, relationships, and important system design considerations is provided. This section describes the key factors involved in fan selection and system design and provides an overview of different types of fans and the applications for which they are generally used. Users already familiar with fan system operation may want to skip this section. The key terms and parameters used in selecting fans, designing systems, and controlling fluid flow are discussed.Section 2: Performance Improvement Opportunity RoadmapThis section describes the key components of a fansystem and the opportunities for performance improve- ments. Also provided is a figurative system diagram identifying fan system components and performance improvement opportunities. Aset of fact sheets describing these opportunities in greater detail follows the diagram. These fact sheets cover:1.Assessing Fan System Needs 2.Fan Types 3.Basic Maintenance 4.Common Fan Systems Problems5.Indications of Oversized Fans 6.System Leaks 7.Configurations to Improve Fan System Efficiency8.Controlling Fans with Variable Loads 9. Fan Drive Options 10.Multiple-Fan Arrangements 11.Fan System EconomicsSection 3: Programs, Resources, and ContactsSection 3 provides a directory of associations andother organizations involved in the fan marketplace, along with a listing of the resources, tools, software, videos, and workshops. AppendicesThe sourcebook includes two appendices. Appendix A is a glossary that defines terms used in the fan system industry. Appendix B presents an overview of the fan system marketplace.The Systems ApproachThe cost-effective operation and maintenance of a fan system requires attention not only to the needs of the individual pieces of equipment, but also to the system as a whole. AÒsystems approachÓ analyzes both the supply and demand sides of the system and how they interact, essentially shifting the focus from individual components to total system performance. Often, operators are so focused on the immediate demands of the equipment that they overlook the broader question of how system parameters are affecting the equipment. The systems approach usually involves the following types of interrelated actions:Establishing current conditions and operating parametersDetermining present and estimating future process production needsGathering and analyzing operating data and developing load duty cyclesAssessing alternative system designs and improvementsDetermining the most technically and economically sound options, taking into consideration all of the subsystemsImplementing the best optionAssessing energy consumption with respect to performanceContinuing to monitor and optimize the systemContinuing to operate and maintain the system for peak performance.Quick Start GuideQuick Start Guide

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Improving Fan System Performance4Axial fans, as the name implies, move an airstreamalong the axis of the fan. The air is pressurized by the aerodynamic lift generated by the fan blades, much like a propeller and an airplane wing. Although they can sometimes be used interchange- ably with centrifugal fans, axial fans are commonly used in Òclean air,Ó low-pressure, high-volume applications. Axial fans have less rotating mass and are more compact than centrifugal fans of compa- rable capacity. Additionally, axial fans tend to have higher rotational speeds and are somewhat noisier than in-line centrifugal fans of the same capacity; however, this noise tends to be dominated by high frequencies, which tend to be easier to attenuate.Fan SelectionFan selection is a complex process that starts witha basic knowledge of system operating requirements and conditions such as airflow rates, temperatures, pressures, airstream properties, and system layout. The variability of these factors and other consider- ations, such as cost, efficiency, operating life, maintenance, speed, material type, space con- straints, drive arrangements, temperature, and range of operating conditions, complicate fan selection. However, knowledge of the important factors in the fan selection process can be helpful for the purposes of reducing energy consumption during system retrofits or expansions. Often, a fan type is chosen for nontechnical reasons, such as price, delivery, availability, or designer or operator familiarity with a fan model. If noise levels, energy costs, maintenance requirements, system reliability, or fan performance are worse than expected, then the issue of whether the appropriate fan type was initially selected should be revisited. Fans are usually selected from a range of modelsand sizes, rather than designed specifically for a particular application. Fan selection is based on calculating the airflow and pressure require- ments of a system, then finding a fan of the right design and materials to meet these requirements. Unfortunately, there is a high level of uncertainty associated with predicting system airflow and pressure requirements. This uncertainty, combined with fouling effects and anticipated capacity expansion, encourages the tendency to increase the specified size of a fan/motor assembly. Designers tend to protect against being responsiblefor inadequate system performance by Òover- specifying.Ó However, an oversized fan/motor assembly creates a different set of operating problems, including inefficient fan operation, excess airflow noise, poor reliability, and pipe/duct vibrations. By describing some of the problems and costs associated with poor fan selection, this sourcebook is intended to help designers and oper- ators improve fan system performance through bet- ter fan selection and improved operating and maintenance practices.Noise.In industrial ventilation applications, noisecan be a significant concern. High acoustic levels promote worker fatigue. The noise generated by a fan depends on fan type, airflow rate, and pressure. Inefficient fan operation is often indicated by a comparatively high noise level for a particular fan type. If high fan noise levels are unavoidable, then ways to attenuate the acoustic energy should be considered. Noise reduction can be accomplished by several methods: insulating the duct; mounting the fan on a soft material, such as rubber or suit- ablespring isolator as required to limit the amountof transmitted vibration energy; or installing sound damping material or baffles to absorb noise energy. Rotational Speed.Fan rotational speed is typicallymeasured in revolutions per minute (rpm). Fan rotational speed has a significant impact on fan performance, as shown by the following fan laws:Introduction to Fan SystemsRPMfinalAirflowfinal= Airflowinitial()RPMinitialRPMfinalPressurefinal= Pressureinitial()2RPMinitialRPMfinalPowerfinal= Powerinitial()3RPMinitial

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A Sourcebook for Industry 5Rotational speed must be considered concurrentlywith other issues, such as variation in the fan load, airstream temperature, ambient noise, and mechanical strength of the fan. Variations and uncertainties in system requirementsare critical to fan type and fan rotational speed selection. Fans that generate high airflow at relatively low speeds (for example, forward-curved blade centrifugal fans) require a relatively accurate estimate of the system airflow and pressure demand. If, for some reason, system requirements are uncertain, then an improper guess at fan rotational speed can cause under-performance or excessive airflow and pressure. Airstream temperature has an important impact onfan-speed limits because of the effect of heat on the mechanical strength of most materials. At high temperatures, all materials exhibit lower yield strengths. Because the forces on shafts, blades, and bearings are proportional to the square of the rotational speed, high-temperature applications are often served by fans that operate at relatively low speeds.Airstream Characteristics.Moisture and particulatecontent are important considerations in selecting fan type. Contaminant build-up on fan blades can cause severe performance degradation and fan imbalance. Build-up problems are promoted by a shallow blade angle with surfaces that allow con- taminants to collect. Fans with blade shapes that promote low-velocity air across the blades, such as backward inclined fans, are susceptible to contaminant build-up. In contrast, radial tip fans and radial blade fans operate so that airflow across the blade surfaces minimizes contaminant build-up. These fans are used in ÒdirtyÓ airstreams and in material handling applications. Corrosive airstreams present a different set of problems. The fan material, as well as the fan type, must be selected to withstand corrosive attack. Also, leakage into ambient spaces may be a concern, requiring the fan to be equipped with a shaft seal. Shaft seals prevent or limit leakage from around the region where the drive shaft penetrates the fan housing. For example, in corrosive environ- ments fans can be constructed with expensive alloys that are strong and corrosion resistant, or they canbe less expensively constructed with fiberglass- reinforced plastic or coated with a corrosion- resistant material. Because coatings are often less expensive than superalloy metals, fan types that work well with coatings (for example, radial fan blades because of their simple shape) are widely used in corrosive applications; however, wear will reducethe reliability of coatings. Alternately, mate- rials such as reinforced fiberglass plastics have been developed for fan applications and function effectively in many corrosive environments. However, there may be size and speed limitations for composite materials and plastic materials.Airstreams with high particulate content levels canalso be problematic for the fan drive train. In direct drive axial fans, the motor is exposed to the airstream. Sealed motors can be used in these applications but tend to be more expensive and, in the event of lost seal integrity, they are suscepti- ble to expensive damage. In axial fans, belt drives offer an advantage by removing the motor from the airstream. In centrifugal fans, the particulate content is less of a factor because the motor or sheave can be located outside of the fan enclosure and connected to the impeller through a shaft seal. Gear drives are occasionally used in applications where speed reduction is required but the use of belt drives is unfeasible because of access or maintenance requirements.In flammable environments, fans are usually constructed of nonferrous alloys to minimize the risk of sparks caused by metal-to-metal contact. In some applications, certain components of the fan can be fabricated out of spark-resistant materials. Fans that operate in flammable environments should be properly grounded, including rotating components, to minimize sparking because of stat- ic discharge. Temperature Range.To a large degree, temperature range determines fan type and material selection. In high-temperature environments, many materials lose mechanical strength. The stresses on rotating components increase as the fanÕs operating speed increases. Consequently, for high-temperature applications, the fan type that requires the lowest operating speed for a particular service is often recommended. Radial blade fans can be ruggedly constructed and are frequently used in Introduction to Fan Systems

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Improving Fan System Performance6high-temperature environments. Component materialsalso significantly influence a fanÕs ability to serve in high-temperature applications, and different alloys can be selected to provide the necessary mechanical properties at elevated temperatures.Variations in Operating Conditions.Applications thathave widely fluctuating operating requirements should not be served by fans that have unstable operating regions near any of the expected operating conditions. Because axial, backward- inclinedairfoil, and forward-curved fans tend tohave unstable regions, these fans are not recom- mended for this type of service unless there is a means of avoiding operation in the unstable region, such as a recirculation line, a bleed fea- ture, or some type of anti-stall device.Space Constraints.Space and structural constraintscan have a significant impact on fan selection. In addition to dimensional constraints on the space available for the fan itself, issues such as mainte- nance access, foundation and structural support requirements, and ductwork must be considered. Maintenance access addresses the need to inspect, repair, or replace fan components. Because down- time is often costly, quick access to a fan can pro- vide future cost savings. Foundation and structural requirements depend on the size and weight of a fan. Selecting a compact fan can free up valuable floorspace. Fan weight, speed, and size usually determine the foundation requirements, which, in turn, affect installation cost. If the available space requires a fan to be locatedin a difficult configuration (for example, with an elbow just upstream or downstream of a fan), then some version of a flow straightener should be considered to improve the operating efficiency. Because non-uniform airflow can increase the pres- suredrop across a duct fitting and will degrade fan performance, straightening the airflow will lower operating costs. For more information, see the factsheet titled Configurations to Improve Fan SystemEfficiencyon page 39.An important tradeoff regarding space and fan systems is that the cost of floor space often motivates designers and architects to configure a fan system within a tight space envelope. One way to accomplish this is to use small-radius elbows,small ducts, and very compact fan assemblies.Although this design practice may free up floor space, the effect on fan system performancecan be severe in terms of maintenance costs. The use of multiple elbows close to a fan inlet or outlet can create a costly system effect, and the added pressure drops caused by small duct size or a cramped duct configuration can significantly increase fan operating costs. System designers should include fan system operating costs as a consideration in configuring fan assemblies and ductwork. Fan Performance Curves Fan performance is typically defined by a plot of developed pressure and power required over a range of fan-generated airflow. Understanding this relationship is essential to designing, sourcing, and operating a fan system and is the key to optimum fan selection.Best Efficiency Point.Fan efficiency is the ratio ofthe power imparted to the airstream to the power delivered by the motor. The power of the airflow is the product of the pressure and the flow, corrected for units consistency. The equation for total efficiency is:An important aspect of a fan performance curve is the best efficiency point (BEP), where a fan operatesmost cost-effectively in terms of both energy efficiency and maintenance considerations. Operating a fan near its BEPimproves its performance and reduces wear, allowing longer intervals between repairs. Moving a fanÕs operating point away from its BEPincreases bearing loads and noise. Another term for efficiency that is often used withfans is static efficiency, which uses static pressure instead of total pressure in the above equation. When evaluating fan performance, it is important to know which efficiency term is being used.Introduction to Fan SystemsTotal Pressure x Airflow Total Efficiency =bhp x 6,362Where:Total Pressure is in inches of water Airflow is in cubic feet per minute (cfm) bhp is brake horsepower

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A Sourcebook for Industry Figure 1-1. Region of Instability57Region of Instability. In general, fan curves arc downward from the zero flow conditionÑthat is, as the backpressure on the fan decreases, the air- flow increases. Most fans have an operating region in which their fan performance curve slopes in the same direction as the system resistance curve. Afan operating in this region can have unstableoperation. (See Figure 1-1.) Instability results from the fanÕs interaction with the system; the fan attempts to generate more airflow, which causes the system pressure to increase, reducing the generated air- flow. As airflow decreases, the system pressure also decreases, and the fan responds by generating more airflow. This cyclic behavior results in a searching action that creates a sound similar to breathing. This operating instability promotes poor fan efficiency and increases wear on the fan components.Fan Start-Up.Start-up refers to two different issues in the fan industry. Initial fan start-up is the commissioning of the fan, the process of ensuring proper installation. This event is important for several reasons. Poor fan installation can cause early failure, which can be costly both in terms of the fan itself and in production losses. Like other rotating machinery, proper fan operation usually requires correct drive alignment, adequate foundation characteristics, and true fit-up to connecting ductwork.Fan start-up is also the acceleration of a fan fromrest to normal operating speed. Many fans, particularly centrifugal types, have a large rotation- al inertia (often referred to as WR2), meaning theyrequire significant torque to reach operating speed. Introduction to Fan Systems5Although fan system curves can have a static component, for the purposes of this sourcebook,system curves pass through (0,0).Slope Lines2,0004,0003,00013,00015,00017,00011,0005,0007,0009,0006,0008,00010,00012,00014,00016,00018,000Region of InstabilitySystemCurves Static Pressure(in. wg)Airflow Rate (cfm) Fan Curve 2624222018161412108642In this region, the slopes of the fan curve and the system curve are near parallel. Instability results when the fan curve intersects the system curve at more than one point, causing the fan to hunt.

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